Liquid crystal display apparatuses for image display are widely used as large-sized displays of flat-screen televisions and monitors, etc. These liquid crystal display apparatuses employ a backlight unit that exits light to a liquid crystal display panel from the back or the lower side of the liquid crystal display panel to enhance the luminance of the display screen. The backlight unit has a lightguide plate and a light-emitting diode (LED) light source disposed at a peripheral side surface of the lightguide plate. The lightguide plate guides light from the light source and emits the guided light from the whole of a light-exiting surface of the lightguide plate toward the liquid crystal display panel that faces the lightguide plate.
Recently, as liquid crystal television systems increase in size, there has been a demand for further reduction in weight and thickness of backlight units used in the television systems. In this regard, as the thickness of a lightguide plate in a backlight unit is reduced, it becomes more likely that color irregularity and luminance unevenness will occur on the light-exiting surface of the lightguide plate. If injection molding is employed as a method of producing a large-sized lightguide plate, it is difficult to fill the resin material throughout the molding tool for the large lightguide plate. This problem can be solved by increasing the injection pressure. This, however, causes an increase in the cost of equipment.
Meanwhile, there has been developed a planar light-emitting device in which a plurality of lightguide plates having respective light sources are arranged side by side or in a matrix, with their respective upper surfaces as light-exiting surfaces being flush with each other to obtain a wide light-exiting surface as a whole (see Japanese Patent Application Publication Nos. Hei 9-186825, 2008-34372, 2006-164625, and 2005-228718).
The above-described conventional planar light-emitting device, however, still has the following problem to be solved. When a plurality of lightguide plates are arranged close adjacent to each other in a backlight unit, a predetermined clearance is provided between each pair of adjacent lightguide plates with possible assembling errors, plate thickness, thermal expansion, etc considered. Meanwhile, the respective peripheral side surfaces of the adjacently disposed lightguide plates are perpendicular to the integrated light-exiting surface of the backlight unit. Therefore, light reaching the peripheral side surfaces of the lightguide plates cannot sufficiently travel toward the light-exiting surfaces. For this reason, the gaps between the mutually adjacent peripheral side surfaces are likely to become dark spots.